Unable to find the sources of your current linux kernel ?
install the following packages:
(dkms for centos7 can be located in the epel repository)
how to install repoforge
rpm -ivh http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el7.rf.x86_64.rpm
how to install epel
yum --enablerepo=extras install epel-release
Pay attention that at the time of this post: EPEL has a dkms version, whereas REPOFORGE (formerly rpmforge) still seems to be slightly in the woods.